I have a 20 LED array that I have arranged with calculations from this website: http://led.linear1.org/led.wiz . There are 10 parallel rows of 2 LEDs each in series with a 270 ohm resistor, running through 12VDC. My aim is to control the brightness of this LED array with one of the PWM pins on the Arduino, using a ULN2803 Darlington Array.
The problem is, when I use PWM and the Darlington, the LEDs are barely lit, even when sending a value of 255 to the PWM output. When I bypass the Darlington and connect the LEDs straight to ground, they glow blindingly bright. I would think that a maximum PWM value would be the same as having no PWM at all, but perhaps this is not the case?
How can I get my array of LEDs to smoothly fade from maximum brightness to dimness?
all help is greatly appreciated, thanks.